It may be helpful to read a few issues of news magazines before choosing your stance on a topic. Once you pick a topic, do the research. Talk to the experts, go to the library, read books, journals, articles. Find out the history of your problem and whom it affects. Know the facts - consider reporting anecdotes and percentages, remembering to attribute this information to the source. When you are researching your topic, be sure to read the pros and cons of your case. You need to be informed of the side against your position, so you can anticipate the reader's objections.
An argumentative essay's thesis statement should include the main reasons for its assertion such as: Because of A, B has not yet been able to prove itself. You must try to interest the reader, never bore them; inform the reader, never confuse them.
Unless your professor instucts you to do so, steer clear of using the first person when writing an argumentative essay. Also, do not begin statements with the words, "I feel," or "I think." We know you are thinking, which is why you are writing.
Get to the main point and speak with authority.